UNDERSTANDING METALLICITY AT HIGH REDSHIFT

UNIVERSEKENTARO MOTOHARA

(IOA, UNIVSERSITY OF TOKYO)

GAS PHASE METALLICITY

GAS PHASE METALLICITY (OXYGEN ABUNDANCE) IS CRUCIAL TO UNDERSTAND GALAXY FORMATION/EVOLUTION, AS IT TRACES THE PREVIOUS STAR FORMATION HISTORY.

WHEN RESOLVED INTO SUB-GALACTIC SCALE, IT ALSO PROVIDES INFORMATION OF

• MASS ASSEMBLY/MERGER

• INFLOW/OUTFLOW

METALLICITY IN THE LOCAL GALAXIES

• METALLICITY IN CLOSE PAIRS ARE SYSTEMATICALLY LOWER THAN IN FIELD SPIRALS (KEWLEY+06)

• METALLICITY GRADIENT IN CLOSE PAIRS SHOWS SHALLOWER GRADIENTS THAN THOSE IN ISOLATED SPIRALS (KEWLEY+10)

⇒ MERGER SUPPLIES LOW-METALLICITY GAS AT OUTER GALAXIES INTO THE CENTRAL REGION ?

Kewley et al. ApJ 721, L48 (2010)

METALLICITY IN MERGER SIMULATION

• MERGER SIMULATIONS SHOW THAT METALLICITY AT A CENTER OF A GALAXY IS LOWERED DURING THE ENCOUNTER

• DUE TO GAS INFLOW2nd pericenter1st pericenter

Rupke et al. ApJL 710, L156 (2010) Montuori et al. A&A 518, A56 (2010)

INVERSE METALLICITY GRADIENT AT Z~1?

• SINFONI/KMOS OBSERVATIONS (QUEYREL+12, STOTT+14)

• METALLICITY FROM N2 INDEX ([NII]6584/H6563)

• INNER PARTS OF GALAXIES SHOW LOWER METALLICITY

• EVIDENCE OF INTERACTION OR COLD STREAM

Stott et al., MNRAS in press (2014)

HOWEVER…WE NEED TO UNDERSTAND

PHYSICAL STATUS OF HII REGIONS

• HI-Z HII REGIONS OCCUPY DIFFERENT REGIONS ON BPT DIAGRAM

Yabe et al., PASJ 64, 60 (2012) Steidel et al., arXiv:1405.5473

HIGHER NE? LARGER U? HARDER EUV?

N2 INDEX IS AFFECTED, THEN

• LARGER EUV OR NE

• SMALLER U

OVERESTIMATE METALLICITY.

Kewley et al., ApJ 774, 100 (2013)

EVOLUTION OF BPT DIAGRAM

CAN BE EXPLAINED BY A EVOLUTION MODEL,

WHERE AT Z~2.5

• 10 TIMES DENSER ELECTRON DENSITY

• 2 TIMES HIGHER IONIZATION PARAMETER

Kewley et al., ApJ 774, L10 (2013)

z=0

z=0.8

z=1.5

z=2.5

IONIZATION FIELD AT LAE/LBG

Z=2-3 LAE/LBG SHOWS 10 TIMES HIGER [OIII]/[OII]

CAN BE EXPLAINED BY 10 TIMES HIGHER IONIZATION PARAMETER

Nakajima & Ouchi, MNRAS 442, 900 (2014)

WHAT’S NEXT?

WE NEED TO UNDERSTAND PHYSICAL STATUS IN HII REGIONS AT HI-Z UNIVERSE

• DENSITY

• IONIZATION PARAMETER

• METALLICITY

• THEIR DISTRIBUTION WITHIN A GALAXY

ELECTRON DENSITY MEASUREMENT

• [OII]3729/3726

• [SII]6731/6716

• DEPENDS ON : HIGHER TEMPERATURE RESULTS IN LOWER DENSITY

METALLICITY MEASUREMENT(DIRECT METHOD)

EMISSION LINE STRENGTH (FROM STATE TO ) AGAINST A HYDROGEN LINE RELATES TO ABUNDANCE WITH THE FOLLOWING RELATION

THEREFORE, OXYGEN ABUNDANCE CAN BE OBTAINED BY• ⇒ (NEGLIGIBLE IN STROMGREN SPHERE)

• ⇒

• ⇒

HOWEVER, COLLISIONAL TRANSITION RATE () STRONGLY DEPENDS ON ELECTRON TEMPERATURE.

ELECTRON TEMPERATURE MEASUREMENT

• FOR DIRECT MEASUREMENT, [OIII]4363 OR [NII]5755 IS NECESSARY

• HOWEVER, THEY ARE EXTREMELY WEAK…

• STACKING MAY GIVES US SOME INSIGHT,ESPECIALLY WHEN METALLICITY IS LOW(AND TEMPERATURE IS HIGH)

METALLICITY MEASUREMENT(EMPIRICAL)

• N2 INDEX : [NII]6584/H6563

• O3N2 INDEX : ([OIII]5007/H4861)/([NII]6584/H6563)

• R23 INDEX : ([OII]3727+[OIII]4959,5007)/H4861

N2 INDEX

• [NII]6584/H6563 : MOST POPULAR

• HIGHER IONIZATION PARAMETER ⇒ LOWER N2

• LARGER ELECTRON DENSITY ⇒ HIGHER N2

• CAN BE USED AT

Denicolo, Terlevich, Terlevich, MNRAS 330, 69 (2002)

O3N2 METHOD

• ([OIII]5007/H4861)/([NII]6584/H6563)

• MEASURE SECONDARY NITROGEN EXCESS (N/O)

• FOR SUPER-SOLAR METALLICITY :

• AGAIN, AFFECTED BY ELECTRON TEMPERATURE (BUT LESS?)

Kewley & Dopita, ApJS 142, 35 (2002) Pettini & Pagel, MNRAS 348, L59

R23 METHOD

• ([OII]3727+[OIII]4959,5007)/H4861

• BIMODAL DISTRIBUTION

• CAN BE SEPARATED IN COMBINATION WITH O3N2 INDEX

• AFFECTED BY IONIZATION PARAMETER

• NEED CORRECTION FOR DUSTEXTINCTION

McGaugh, ApJ 380, 140 (1991)

IONIZATION PARAMETER

[OIII]5007/[OII]3727 WILL BE A GOOD INDICATOR

NEED CORRECTION FOR DUST EXTINCTION

Nakajima & Ouchi, MNRAS 442, 900 (2014)

METALLICITY MEASUREMENT(EMPIRICAL)

• N2 INDEX : [NII]6584/H6563

• O3N2 INDEX : ([OIII]5007/H4861)/([NII]6584/H6563)

• R23 INDEX : ([OII]3727+[OIII]4959,5007)/H4861

ALL THE INDICES MAY REQUIRE CORRECTION FOR DIFFERENT ENVIRONMENT

OBSERVATIONS OF ALL THE EMISSION LINES ARE NECESSARY TO SOLVE THE PROBLEM

IFU SURVEY OF Z=1-2 GALAXIES

• VARIOUS GALAXIES AT Z=1~2

• SAMPLES MAYBE SUPPLIED BY EXISTING SURVEYS(SXDS, GOODS-N, SDF) AND NEWLY PLANNED SWIMS-18 SURVEY (ON TAO/SUBARU)

• COVER WHOLE MAJOR OPTICAL EMISSION LINES

• [SII]6731/6716

• H6563+[NII]6584

• [OIII]5007

• H4861

• ([OIII]4363) : POSSIBLY BY STACKING?

• [OII]3729/3726

• SPECTRAL RESOLUTION SHOULD BE ENOUGH TO RESOVE [OII] : R>3000

SENSITIVITY OF ULTRA-SUBARU

• MAX 1.8ARCSEC FOV/STARBUG ⇒ 12KPC DIAMETER

• 0.2ARCSEC SAMPLING ⇒ 1.4KPC 7KPC DIAMETER SPLIT INTO 19 FIBERS

• REPLACEMENT OF DETECTORS AND GRISMS MAY PROVIDE BETTER SENSITIVITY BY ~1.5MAG

• STILL, SENSITIVITY IS A BIG PROBLEM : NEED TO BE BRIGHTER BY ~2MAG THAN NORMAL SPECTROSCOPIC TARGETS

⇒ POSSIBLE TARGETS WILL BE THOSE WITH KAB<21

SWIMS

SIMULTANEOUS-COLOR WIDE-FIELD INFRARED MULTI-OBJECT SPECTROGRAPH

• 1ST GENERATION INSTRUMENT FOR TAO 6.5M

• FOV OF 9.6’Φ ON TAO

• 2-BAND SIMULTANEOUS IMAGING AT 0.9～1.4 / 1.4～2.4MICRON

• CAPABLE OF R=1000 SPECTROSCOPY FROM 0.9 TO 2.5 MICRON IN A SINGLE SHOT

• CAPABLE OF MOS SPECTROSCOPY FOR MAX 40 OBJECTS

• WILL BE CARRIED INTO SUBARU AS A PI INSTRUMENT IN FY2015

S W I M S

SWIMS-18

• WIDE FIELD SURVEY USING 18 FILTERS

• 9 MBFS, 6 NBFS, 3 BBFS

• 1SQ.DEGREE FOV

• MBF SURVEY

• ACCURATE PHOTO-Z AT Z=1-3

• 1.2E7 MPC3 VOLUME

• NBF SURVEY

• DUAL LINE EMITTER SURVEY (HA/[OIII], ETC)

• 7.5E5 MPC3 VOLUME

ANSWERS TO QUESTIONS(Q1) WHAT IS THE OPTIMUM SPATIAL SAMPLING (OR DIAMETER IN ARCSEC OF EACH FIBER IN THE BUNDLE) AND FOV OF THE BUNDLE?

LARGER FOV PER BUNDLE IS PREFERABLE0.2ARCSEC (~1.4KPC) IS ENOUGH

(Q2) WHAT IS THE OPTIMUM AND MINIMUM NUMBER OF THE FIBER BUNDLES (OR MULTIPLICITY) IN THE 13'.6 DIAMETER FOV?

NUMBER DENSITY OF KAB<21 MAG Z=1-2 GALAXIES IS ~0.2/ARCMIN^2,

THEREFORE, THE OPTIMUM NUMBERS IS ~30.

HOWEVER, THEY CAN BE COVERED WITH MULTIPLE SHOTS, SO THE MINIMUM NUMBER CAN BE THAT OF THE BASELINE SPECIFICATION (16 WITH 1.8ARCSEC FOV).

(Q3) WHAT IS THE CRITICAL WAVELENGTH RANGE IN NEAR-INFRARED COVERED BY THE STARBUG SYSTEM (0.9-2.0MICRON)?

FULL RANGE OF 0.9-2MICRON IS NECESSARY TO SAMPLE ALL THE IMPORTANT OPTICAL EMISSION LINES FROM [OII]3727 TO [SII]6731 AT REDSHIFT UPTO ~2.

(Q4) WHAT IS THE OPTIMUM SPECTRAL RESOLUTION?

R=3000 IS PREFERRED TO RESOLVE VELOCITY FIELD OF THE GALAXY AS WELL AS TO RESOLVE [OII]3726/3729.

HOWEVER, WIDE WAVELENGTH COVERAGE IS ANOTHER IMPORTANT FEATURE FOR EFFECTIVE OBSERVATION. IT WILL BE NICE IF ZJ OR HK SPECTRUM CAN BE TAKEN WITH A SINGLE SHOT.

(Q5) WHAT IS THE SENSITIVITY REQUIREMENT FOR THE PHASE-I INSTRUMENT?

KAB~22.5 PER FIBER

(Q6) PLEASE DESCRIBE A BRIEF OBSERVATION PLAN FOR YOUR SCIENCE CASE WITH THE FIBER BUNDLE MULTI-OBJECT IFU.

- NUMBER OF OBJECTS / SURVEY AREA : TBD

- FIELDS : SWIMS-18 FIELD, SXDS, GOODS-N ….

- NUMBER OF NIGHTS TO COMPLETE YOUR SURVEY : TBD, 1 POINTING/NIGHT?

- UNIQUENESS

(Q7) HOW COULD THE PROPOSED SCIENCE CASES BE COMPETITIVE OR COMPLEMENTARY TO THE SCIENCE WITH 30M CLASS TELESCOPES (E.G. TMT) OR SPACE TELESCOPES (E.G. JWST) IN 2020S?

THE PROPOSED OBSERVATIONS CAN BE CARRIED OUT ONLY FOR THE BRIGHTEST OBJECTS BY 8M CLASS TELESCOPES, WITH COARSE (>1KPC) SAMPLING.TMT WILL PROBE GALAXIES WITH L* OR FAINTER LUMINOSITY, WITH HIGHER SPATIAL RESOLUTION.

(Q8) PLEASE DESCRIBE THE REQUIREMENTS FOR PHASE-II INSTRUMENT (STARBUGS + DEDICATED SPECTROGRAPH) TO DEVELOP YOUR SCIENCE CASE.

• FIBER BUNDLE CONFIGURATIONS : 0.2”/FIBER, FOV OF EACH BUNDLE LARGER THAN 1.8ARCSEC, # OF BUNDLES ~30

• WAVELENGTH COVERAGE : 0.7 TO 2.0 MICRON

• SPECTRAL RESOLUTION : R=3000

• SENSITIVITY : KAB=22.5MAG/FIBER (WHEN BINNED DOWN TO R~500)

(Q9) WHAT IS THE UNIQUE POINT OF THE FIBER BUNDLE MULTI-OBJECT IFU WITH STARBUGS COMPARED TO THE IMAGER OR MULTI-OBJECT SLIT SPECTROGRAPH?

HIGH EFFICIENCY SURVEY SPEED WITH MULTI-OBJECT IFU CAPABILITY.